Electric motor/gear mechanism unit

ABSTRACT

The invention relates to an electric motor/gear mechanism unit including a housing, an iron-free rotor winding rotatably arranged in the interior of the housing, a collector connected to the rotor winding, a rotor shaft extending through the collector, and a gear mechanism which is connected to the rotor shaft and which has an output shaft. The present invention is so conceived that the gear mechanism is produced from a non-magnetic material and arranged in the interior of the rotor winding.

This application is a continuation of prior application Ser. No.13/120,859 filed Aug. 22, 2011, which is a National Stage of ApplicationNo. PCT/EP2009/008518 filed Nov. 30, 2009, which claims priority toIsrael Application No. 195613 filed on Nov. 30, 2008, the entirecontents of each of which are incorporated by reference herein.

The invention relates to an electric motor/gear mechanism unit accordingto the preamble of claim 1.

Electric motor/gear mechanism units according to the prior art are knowne.g. from U.S. Pat. Nos. 4,918,344, 5,662,545, 6,500,087, 7,211,016,U.S. 2004/0095037 and GB 1007524A. The electric motor/gear mechanismunits described there have a common housing for the electric motor andthe gear mechanism. In many fields of use, there is an increasing demandfor extremely compact electric motor/gear mechanism units, in particularfor those having a high torque. There is an ever increasing demand for acompact structural design of the axial as well as of the radialdimensions of electric motor/gear mechanism units. The electricmotor/gear mechanism units known from the prior art can no longersatisfy future demands and some of them require a high productionoutlay.

It is therefore the object of the present invention to provide anextremely compact electric motor/gear mechanism unit having a hightorque. This object is achieved by the features of claim 1. Theinvention starts from an electric motor/gear mechanism unit comprising ahousing, an iron-free rotor winding rotatably arranged in the interiorof the housing, a collector connected to the rotor winding, a rotorshaft extending through the collector, and a gear mechanism which isconnected to the rotor shaft and which has an output shaft. A solutionaccording to the present invention is provided when the gear mechanismis arranged in the interior of the rotor winding, and when it consistsexternally of an annulus gear, which is preferably produced from amagnetic material, whereas the movable parts of the gear mechanism areproduced from a non-magnetic material. Electric motors with an iron-freerotor winding normally have a very compact structural design in theradial direction. Making use of the solution according to the presentinvention a very compact structural design of the whole electricmotor/gear mechanism unit is achieved also in the axial direction. Dueto the fact that the annulus gear is produced from magnetic material, italso serves as a magnetic yoke for the magnetic circuit of the motor.The magnetic field of the permanent magnet will hardly enter theinterior of the gear mechanism, when the gears meshing with the annulusgear are produced from a non-magnetic material. Losses caused by areversal of magnetism, eddy currents and magnetic pressure forces areavoided in this way. In addition, the dual function of the gearmechanism housing can be used insofar as there will be more room for thegear mechanism, which means that the gear mechanism can be provided witha more stable structural design.

Advantageous further developments of the present invention are thesubject matter of the subclaims.

According to a preferred embodiment of the present invention, a hollowpermanent magnet is arranged in the interior of the rotor winding. Thishollow permanent magnet is connected to the housing of the electricmotor and defines thus the stator of the electric motor. The hollowpermanent magnet encloses the gear mechanism of the electric motor/gearmechanism unit. On the basis of this structural design, very highdegrees of efficiency of the electric motor and, consequently, of theentire electric motor/gear mechanism unit can be achieved.

Alternatively, the hollow permanent magnet may also be arranged outsideof the rotor winding so that it encloses the rotor winding. In thiscase, the hollow permanent magnet can define the housing of the electricmotor/gear mechanism unit. If an additional housing should be provided,it can be produced from a magnetic material and thus define a magneticyoke.

According to another preferred embodiment of the present invention, therotor shaft and the output shaft are in alignment with one another.

In accordance with another preferred embodiment, the gear mechanism is aplanetary gear unit. Planetary gear units allow a realization ofextremely high reduction ratios in combination with a compact structuraldesign. Alternatively, spur gear units or bevel gear units may be usedas well.

According to another preferred embodiment of the present invention, theplanetary gear unit is configured such that it comprises at least onestage. The first gear stage of a planetary gear unit, which is connectedto the rotor shaft, normally has applied thereto the highest loads. Eachgear stage of planetary gear unit comprises a planetary carrier which isrotatable about an axis of rotation, a sun gear, an annulus gear and atleast one planet gear. The end face of the planetary carrier is providedwith a journal for each planet gear, said journal projecting from saidend face and the planet gear being rotatably supported thereon by meansof an axial bore. In view of manufacturing tolerances, high frictionlosses may occur between planet gears and the sun gear and annulus gear,respectively. This leads to a generation of a large amount of heat andto a short service life of the planetary gear unit. The friction lossescan be reduced, when there is a certain amount of play between theplanet gears and the sun gear and annulus gear, respectively. This ispreferably achieved in that the planet gears are radially displaceablewith respect to the axis of rotation of the planetary carrier. To thisend, the journals of the planetary carrier are preferably implementedsuch that they have a substantially elliptical cross-section. Theshorter one of the two principal axes of the ellipse extends in theradial direction of the planetary carrier. The measures for providing acertain amount of play between the planet gears and the sun gear andannulus gear, respectively, are preferably taken for the first stage ofthe planetary gear unit. They may, however, also be taken for the otherstages of the planetary gear unit, if the planetary gear unit shouldcomprise more than one gear stage. The play provided reduces thefriction losses. This will also lead to a reduction of heat developmentand to a longer service life of the gear mechanism.

According to another preferred embodiment of the present invention, therotor shaft has, on its end facing the gear mechanism, external teethdefining the sun gear of the first gear stage of a planetary gear unit.The outer diameter of said external teeth of the rotor shaft correspondsto the diameter of the rotor shaft itself. In the case of thisembodiment, a pinion, which normally defines the sun gear of the firstgear stage, need not be attached to the rotor shaft. The diameter of thesun gear is therefore smaller than in the case of an attached pinion. Itis thus possible to accomplish a higher reduction ratio, whereby thetorque of the electric motor/gear mechanism unit is increased.

According to a preferred embodiment, at least the teeth of the gears ofthe first gear stage are hardened or provided with a hard layer. In thecase of non-magnetic metallic materials, said hardening can be carriedout by means of a surface treatment, such as a chemical or a thermaltreatment. This will increase the service life of the gear mechanism. Inview of the high production costs for hardening or coating processes,the latter are only carried out in the first, highly loaded gear stageof the planetary gear unit. A suitable base material is e.g.non-magnetic steel. Alternative materials for the gears of the gearmechanism are particularly hard plastic materials, metallic glass orceramic materials.

The service life of the electric motor/gear mechanism unit can beincreased still further, when the housing is provided with cooling finsand/or with internal and/or external cooling channels for improved heatdissipation. The heat of the gear mechanism, the permanent magnet andthe rotor winding is transferred to the housing via the air gap betweenthe rotor and the stator. An improved dissipation of heat isaccomplished, when the bearing seat of the rotor or of the rotor shafthas a large contact area.

In view of the fact that the service life of the electric motor exceedsthat of the gear mechanism many times, even if more intensive measuresare taken for increasing the service life of the gear mechanism, thegear mechanism is preferably adapted to be replaced and/or relubricated.

According to another preferred embodiment of the present invention, thegear mechanism is filled with oil so as to increase its service life.

Hollow-cylindrical permanent magnets are comparatively expensive toproduce. According to another preferred embodiment of the presentinvention, the hollow stator permanent magnet is therefore composed ofmagnet segments. This allows production at a reasonable price.

In order to accomplish a better guidance of the rotor or the rotorwinding and in order to avoid the rotor winding from rubbing againstcomponents of the stator, the rotor shaft is supported such that it isaxially preloaded by means of a spring or a spring plate 35. To thisend, a preloaded bearing seat is preferably provided in the brush cover.

In the case of the electric motor/gear mechanism unit according to thepresent invention, various electric motors can be used. It is imaginableto use e.g. alternating current as well as direct current motors,mechanically commutated or brushless motors and stepping motors.

In the following, a preferred embodiment of the present invention willbe explained in more detail making reference to the drawings, in which:

FIG. 1 shows an oblique view, part of which is a sectional view, of anelectric motor/gear mechanism unit according to the present invention;

FIG. 2 shows a straight longitudinal sectional view of the electricmotor/gear mechanism unit according to the present invention shown inFIG. 1;

FIG. 3 shows the planetary carrier of the first stage of the planetarygear unit of the electric motor/gear mechanism unit according to thepresent invention as shown in FIGS. 1 and 2;

FIG. 4 shows a straight longitudinal sectional view of the electricmotor/gear mechanism unit according to the present invention shown inFIG. 1; and

FIG. 5 shows a straight longitudinal sectional view of the electricmotor/gear mechanism unit according to the present invention shown inFIG. 1.

FIGS. 1 and 2 show an electric motor/gear mechanism unit 20 according toa preferred embodiment of the present invention. The electric motor/gearmechanism unit 20 essentially comprises a bell-type armature motor withan iron-free rotor winding 2 of a known structural design, and aplanetary gear unit 9 installed in the interior of the hollowcylindrical bell-type armature motor. The housing 1 of the electricmotor/gear mechanism unit 20 according to the present invention has abrush cover-side end 15 and an output-side end 16. At the out-put-sideend 16 the housing 1 merges with a neck portion 18 via an area ofreduced width 17. In the interior of the housing 1 and concentricallytherewith, an iron-free rotor winding 2 is arranged. This iron-freerotor winding 2 is connected via the collector 4 to the rotor shaft 10,coaxially with said rotor shaft and such that it is secured againstrotation relative thereto. At the brush cover-side end 15 of the housing1, the housing 1 is closed by a brush cover 12. The whole rotorincluding the iron-free rotor winding 2 is rotatably supported in thebrush cover via the bearing 6 such that it is concentric with thehousing 1. In the direction of the output-side end 16 of the housing,the rotor shaft 10 is, in addition, rotatably supported, via the bearing5, on the hollow permanent magnet 3, which is connected to the housing 1such that it is secured against rotation relative thereto. The rotorshaft 10 is supported in the bearing 5 via a small step-shaped flange 23of the rotor shaft 10. The hollow cylindrical permanent magnet 3 extendsaround an annular support wall 26 after the fashion of a sleeve and isenclosed by an iron-free rotor winding 2. Between said iron-free rotorwinding 2 and the hollow cylindrical permanent magnet 3 a small air gapis formed. In FIG. 1 it can be seen that the bell-type armature motor isconfigured as a brush-commutated motor. The commutation is effected viatwo carbon brushes 11 which slide over the collector 4 and which areheld by the brush holders 21 and 22. The electric connection of the twocarbon brushes 11 is established via the two connection cables 24.

On the rotor shaft end facing the interior of the electric motor/gearmechanism unit a pinion 13 defines the sun gear of the first gear stageof a four-stage planetary gear unit 9. The annulus gear 28 which thefour gear stages have in common also defines the housing of theplanetary gear unit 9. It follows that the planetary gear unit 9 definesan independent unit and can be installed in the interior of thebell-type armature motor in a fully mounted condition. The annulus gear28 of the planetary gear unit 9 abuts on the annular support wall 26 ofthe housing 1 of the electric motor/gear mechanism unit 20 such that itis concentric and flush with said support wall 26. In FIG. 2, the planetgears of the gear stage are designated by reference numeral 9A, theplanet gears of the second gear stage by reference numeral 9B, those ofthe third stage are, in a corresponding manner, designated by 9C, andthose of the fourth stage by 9D. Furthermore, the planetary carriers ofthe first, second, third and fourth stages are sequentially designatedby reference numerals 31, 32, 33 and 14. The planetary carriers of thefirst, second and third stages are connected to the sun gear of therespective subsequent stage. The planetary carrier 14 of the fourthstage simultaneously defines the flange for the output shaft 7 whoseaxis coincides with the axis of the rotor shaft 10. The output shaft 7is rotatably supported via two bearings 8 in the neck portion 18 of thehousing 1 of the electric motor/gear mechanism unit 20. All the sungears, planet gears and planetary carriers of the planetary gear unit 9are produced from non-magnetic materials so as to avoid interferenceand/or losses during operation of the electric motor/gear mechanismunit. In addition, the highly loaded first stage of the planetary gearunit 9 is provided with toothings hardened by surface finishing. Alsothe other components of the planetary gear unit 9, in particular thecomponents of the other stages of the planetary gear unit, may at leastbe surface hardened or produced from particularly wear resistantnon-magnetic materials. Reference should be made to the fact that,depending on the desired reduction ratio or depending on the desiredtorque of the output shaft 7, also planetary gear units comprising oneto three stages may be used. Theoretically, it would also be possible touse a planetary gear unit comprising five or more stages, but thefriction losses in the case of planetary gear units comprising five ormore stages are so high that such planetary gear units are normally notused.

In FIG. 3 the planetary carrier 31 of the first gear stage of theplanetary gear unit 9 is shown. In order to reduce the friction and theheat development in the first stage, the planet gears 9A of the firstgear stage are intentionally supported with a certain amount of play.This intentional play is a play in the radial direction with respect tothe axis of rotation 29 of the planetary carrier 31, which, due to thecoaxial arrangement of the motor and the gear mechanism and due to theengagement of the pinion 13, coincides with the axis of rotation of therotor shaft 10. Each of the planet gears 9A of the first gear stage isrotatably supported on a respective journal 27 of the planetary carrier31 by means of a hollow cylindrical bore, said journals 27 being shownin FIG. 3. The journals 27 extend perpendicularly from the end face ofthe planetary carrier 31 parallel to the rotor shaft 10 and to the wholelongitudinal axis of the electric motor/gear mechanism unit 20. Thecross-section of the journals 27 is elliptical so that the shorterprincipal axis of the elliptical cross-section extends radially withrespect to the axis of rotation 29 of the planetary carrier 31. Thelonger principal axis of the ellipse corresponds approximately to thediameter of the axial bore of the planet gears 9A. It follows that theplanet gears 9A are supported with play in the radial direction withrespect to the axis of rotation 29 of the planetary carrier 31. Due tothe fact that they are supported with play, their optimum position withrespect to the sun gear 13 of the first stage and the annulus gear 28will be obtained automatically on the basis of the tolerances. Whereasin the case shown, three planet gears and three journals are provided,it is also possible to provide a different number of planet gears perstage. The embodiment that has been chosen in FIG. 3 for the planetarycarrier 31 of the first gear stage of the planetary gear unit 9 can alsobe chosen for the other stages.

When the service life of the old planetary gear unit 9 has come to anend, said old planetary gear unit 9 can be removed from the electricmotor/gear mechanism unit as a separate subunit so that a new planetarygear unit 9 can be installed into the electric motor/gear mechanism unit20. In addition to the already discussed measures taken for increasingthe service life of the planetary gear unit 9, the planetary gear unitmay also be completely filled with oil so as to accomplish an improvedheat transfer. The oil also serves the purpose of lubrication. Coolingand heat dissipation of the electric motor/gear mechanism unit 20 iseffected via cooling fins of the housing 1, which are shown in FIG. 4.Cooling can be improved still further through cooling channels in thehousing 1.

1. An electric motor/gear mechanism unit comprising: a housing, aniron-free rotor winding rotatably arranged in an interior of thehousing, a collector connected to the rotor winding, a rotor shaftextending through the collector, and a gear mechanism which is connectedto the rotor shaft and which has an output shaft, wherein the gearmechanism is arranged in an interior of the rotor winding with anexternal, internally toothed annulus gear, and wherein gears of the gearmechanism are produced from a non-magnetic material, the housing and theannulus gear being formed of a magnetically soft material.
 2. Anelectric motor/gear mechanism unit according to claim 1, wherein ahollow permanent magnet is arranged in the interior of the rotorwinding.
 3. An electric motor/gear mechanism unit according to claim 1,wherein the rotor shaft and the output shaft are in alignment with oneanother.
 4. An electric motor/gear mechanism unit according to claim 1,wherein the gear mechanism is a planetary gear unit.
 5. An electricmotor/gear mechanism unit according to claim 4, wherein the planetarygear unit is configured such that it comprises at least one stage, eachgear stage comprising a planetary carrier which is rotatable about anaxis of rotation, a sun gear, an annulus gear and at least one planetgear, an end face of the planetary carrier further being provided withat least one journal which projects therefrom and on which the planetgear is rotatably supported, and at least said at least one planet gearof a first gear stage being implemented such that it is at leastradially displaceable relative to an axis of rotation of the planetarycarrier.
 6. An electric motor/gear mechanism unit according to claim 5,wherein at least said at least one journal of the planetary carrier ofthe first gear stage has a substantially elliptical cross-section.
 7. Anelectric motor/gear mechanism unit according to claim 5, wherein therotor shaft has, on its end facing the gear mechanism, external teethdefining the sun gear of the first gear stage, an outer diameter of saidexternal teeth of the rotor shaft corresponding to a diameter of therotor shaft.
 8. An electric motor/gear mechanism unit according to claim5, wherein at least the teeth of the gears of the first gear stage arehardened or provided with a hard layer.
 9. An electric motor/gearmechanism unit according to claim 1, wherein the housing is providedwith cooling fins and/or with internal and/or external cooling channels.10. An electric motor/gear mechanism unit according to claim 1, whereinthe gear mechanism is configured to be replaced and/or relubricated. 11.An electric motor/gear mechanism unit according to claim 1, wherein thegear mechanism is filled with oil.
 12. An electric motor/gear mechanismunit according to claim 2, wherein the hollow permanent magnet iscomposed of magnet segments.
 13. An electric motor/gear mechanism unitaccording to claim 1, wherein the rotor shaft is supported such that itis axially preloaded by a spring or a spring plate.